This invention relates to a tension providing mechanism availing a spring torque. The tension providing mechanism means a mechanism which acts a pushing force in a fixed direction continuously and displays the properties of nearly a rigid body when a reaction force acts thereon. Such mechanism is, for instance, used when the rigid body properties are requested as in such case of pressing a chain, a belt or the like with a force having a fixed direction like a chain tensioner or a belt tensioner etc. or of acting the reacting force against said tensioner.
In other words, the chain tensioner provides a fixed tension to the chain by pressing the chain in a fixed direction when said chain occurs the slackness by elongation or abrasion during the use. In this case, the properties of nearly a rigid body are desirable for the reaction force against the pressing direction.
Heretofore, in chain tensioner, for instance, there exist two types, a type of manual control with manual adjustment according to the elongation of the chain and a type of automatic control. The former is comparatively cheap, but has such defects as difficulty in maintenance and generation of an abnormal sound, while the latter has such defects as the complication of the whole mechanism and high cost since it avails an oil pressure.
Heretofore, there exists a tension providing mechanism having no necessary maintenance (Japanese patent application No. 1966-22309) as shown in FIG. 1. In locking mechanism of this device however, the outer circumference of a piston 21 is only pressed with a push or set screw 27. Accordingly, the locking in the pushing direction (direction shown with an arrow) is uncertain and the screw 27 is apt to fall off. Further, when this device is incorporated into other apparatus, an oil leakage from the screw portion 27 occurs or a crack appears on the sliding surface since the sliding portion of the piston 21 is pressed with a push screw directly, thereby causing a wear. Furthermore, when the pushing screw 27 is incorporated into the device, its controlling is impossible. Therefore, the exposed portion of the device increases, whereby making the device compact is impossible.
Still further, since the locking or unlocking condition of the pushing force in said device can not be confirmed from outside, said device has such defects as taking much time in assembling, incorporation into an apparatus or a periodical inspection and controlling. In FIG. 1, the numeral 22 is a cylinder, 23 is a shoe integrated with a piston 21, 24 is a male screw, 25 is a spiral spring and 26 is a fixed pin.